The present invention relates to an ultrasound transducer, comprising at least one piezoelectric body with at least one lower and one upper electrode and a coupling layer with on a wafer surface on which the ultrasound transducer is disposed and connected to the lower electrode and to a method of manufacturing such an ultrasound transducer.
Like in many areas of electronic devices and sensors, the components for the apparatus and the systems continue to become smaller and more powerful also for ultrasound systems. An important part of such systems are ultrasound sensors, which, in most cases, are designed specifically for a particular measuring problem. Costs and quality of components are both very important in the development of ultrasound systems. It is essential that in multi-transducer systems the ultrasound transducers have all the same acoustical and electrical properties.
Examples for the high development state of ultrasound testing equipment are ultrasound transducer arrays or also group transducers. A transducer array comprises a number of individual transducer elements, preferably columns or strips which, for physical reasons, must be very small and arranged tightly adjacent one another in order to deflect the acoustic signal into the desired direction for example by a phase-modified control of the individual transducer elements or groups. The size of such individual transducer elements and their distances from one another are below 0.5 mm at a frequency of the transducer elements of 5 MHz.
With such arrangements, it is possible to swipe the medium to be examined without changing the position of the ultrasound transducer head. The transducers may then be disposed in a linear array or in a matrix structure. This type of ultrasound transducers are often used in material testing and for medical applications.
[2] discloses, for example in connection with the use of ultrasound computer tomography (USCT) for early breast cancer detection, a special arrangement of the newest generation of ultrasound transducers of the type referred to above. For such a system, a large number of ultrasound transducers of small size (for example, 1×1 mm) is required, which are effective, approximately, as point-like radiation emitters. They are arranged around an examination volume as a matrix structure in the form of a cylinder or in the form of a semi-sphere whereby spatial information (3D) can be obtained from the volume to be examined without mechanical movement of any of the ultrasound transducers. This measuring arrangement in connection with a parallel signal processing unit is suitable for a complete tomographic examination of a body part of a patient with measuring times of less than 0.05 s, so that a chronology if individual images is really becoming negligibly important. The high number (several thousands) of ultrasound transducers of small size corresponds in principle to a cylinder shaped or sphere-shaped ultrasound transducer array with the individual ultrasound transducers forming the transducer elements.
The acoustic properties depend physically directly on the geometric data of ultrasound transducers, particularly the coupling layer and transducer element (usually a piezo-electric body). Manufacturing accuracies and tolerance ranges in the production of ultrasound transducers affect the accuracy and tolerance width of acoustic properties of an ultrasound transducer manufacturing series. Even though small deviations of the acoustic properties can be compensated for electronically within a certain bandwidth or can be limited by a subsequent quality control, it is necessary already for economical reasons that the ultrasound transducers have predetermined acoustic and electric properties within a narrow tolerance widths.
The coupling- or adaptation layer is provided for a low-loss coupling of a transducer element to a medium. It compensates for different acoustic impedances of a transducer and of water, wherein the thickness of this layer is ideally ¼ of the wavelength of the thickness resonance frequency of the piezo electric body (transducer). Such layers are generally produced from corresponding casting materials which are applied during manufacture to the transducer element which is already contacted and electrically connected. This is followed generally by an adaptation of the coupling layer thickness to the frequency (wavelength) of the transducer element by means of mechanical and therefore expensive follow-up working or fine-cutting of the coupling layer. In accordance therewith, the manufacture of most ultrasound transducers follows a strategy from the inside to the outside, that is, it starts with the transmitter element.
[1] discloses, based on a simple manufacturing capability, an ultrasound transducer and a method of manufacturing such a transducer. In the radiation direction, a piezo-electric body (transducer element) includes a contact area on which a coupling layer is disposed. The contacts on the opposite electrode surface of the body, on the other hand, is provided by a conductor foil which is cemented or pressed onto the electrode surface. The conductor foil is held pressed in contact with the electrode surface for example mechanically by an attenuation body. With the arrangement of the conductor layers on the conductor foil, individual areas of the body or of the transducer are selectively controllable. The electrode at the radiation emitting side itself does not include any conductor structure.
Such an ultrasound transducer still requires a coupling layer which is mounted as a separate component onto the electrode at the radiation emitting side. Furthermore, the connections to the two electrodes are established by individual wire connections which requires a comparatively high manufacturing expenditures.
In [3] an ultrasound transducer system is described wherein several piezo-ceramic bodies, each with an electrode surface are cemented over an area directly onto a conductor plate. The electrodes are connected to sender and receiver electronics on adjacent conductor plates via bonded wires.
Based on this state of the art, it is the object of the present invention to provide an ultrasound transducers which generally facilitates the manufacture thereof, that is, specifically, which provides for an improved accuracy and quality of the coupling layer with smaller tolerance ranges.